A laterite (nickeliferous) ore body essentially contains three fractions: the limonite fraction beneath surface soil, the saprolite fraction above the bed rock, and ores in the transitional zone between limonite and saprolite. The nickel-containing mineral in limonite is goethite and/or hematite, which are soft and fine in particle size. The nickel-containing minerals in saprolite are mostly coarse siliceous phases such as serpentine, garnierite, chlorite, nontronite, and smectite. The ore in transition zone contains both limonite and saprolite. With the aid of geological data and mining program, it is possible to separate limonite and saprolite via screening with designed cut-off particle size. However, in mining practice, it is difficult to have a clean separation of limonite and saprolite fractions. Consequently, the cross-entrainment of limonite and saprolite exists to a certain extent with the run-of-mine saprolite and limonite fractions.
PCT/AUO3/00309 (H. Liu et al, QNI Technology PTY LTD) describes an Atmospheric Acid Leach (AAL) process that processes the whole laterite ore deposit across the three ore zones. In the process described the limonite slurry (or the low Mg containing fraction) was mixed and leached with concentrated acid at temperatures up to 105° C. (or the boiling point at atmospheric pressure). The iron content in the tested limonite in the Examples of this application was generally from 40-43%, and the dose of sulfuric acid, in terms of the weight ratio of sulfuric acid to dry limonite ore, was 1.32 to 1.43. This is shown in each of the eleven Examples. At the equilibrium acidity of 0-10 g/L to form goethite, the saprolite (or the high Mg containing fraction) used showed good leaching reactivity and neutralization capacity. This was due to the fact that it was not significantly contaminated with limonite.
The mineralogy of laterite ore components varies depending upon from which region the ore is sourced. Table 1, in PCT/AU03/00309 shows the characterisation of various laterite ore bodies from different parts of the world. The ore which is used in the Examples of PCT/AU03/00309 was sourced from Gag Island, Indonesia. Because of the wide characterisation of different laterite ore bodies, the process to recover the nickel and cobalt from within the ore body must be tailored to maximise the recovery.
The Applicants have found that with a laterite ore body with high iron content, particularly a high iron content in the limonite fraction and a high goethite and/or hematite content in the saprolite fraction, the nickel recovery is compromised in an atmospheric leach process as the saprolite fraction has less leaching reactivity and neutralisation capacity. This is thought to be due to a higher goethite or hematite content in the saprolite fraction.
The present invention aims to overcome or alleviate some of the problems that may occur when processing a high iron content laterite under atmospheric pressure conditions.
A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.